SMC sierra monitor corporation Sentry Instruction Manual - Version 6
SERVICE
Page: 77
1. Confirm that system power has been
removed.
2. Remove the transmitter electronics board
from the main housing and unplug the
sensor harness from the transmitter
electronics.
3. Unscrew the sensor housing from the
bottom of the enclosure
4. Hold the sensor assembly so that the
harness faces down and the sensor faces
up. Unscrew and remove the round
section of the housing from the hex
section. Be careful not to lose the spacer
washer which will be sitting on top of the
exposed sensor.
5. Carefully pull the old sensor straight up
from the socket.
6. Orient the new sensor so that the sensor
pin labeled “C” faces the socket labeled
“C” which is on the far side of the board
from the vertical reed switch. The reed
switch will slide into a hole on the side of
the new sensor. Press the new sensor’s
pins into the three sockets.
7. Carefully replace the cover on the sensor
assembly including the spacer washer.
8. Install the sensor assembly into the enclosure and
tighten firmly.
9. Reconnect the sensor harness to the transmitter,
install the transmitter into the housing and restore
power.
10. Allow one hour for the sensor to stabilize prior to
recalibration.
11. Recalibrate the sensor module.
7.8.3.3 SENSOR OUTPUT ADJUSTMENT
The following procedure is to be used when, during
normal calibration of a new sensor, the span voltage
cannot be adjusted to a high enough level.
1. Adjust the span potentiometer so that it is
approximately mid range. (Twenty turns
clockwise and tens turns counter-clockwise).
2. Remove system power and remove both the
transmitter and the sensor assembly from the
enclosure. Remove the sensor assembly cover so
that the sensor is visible.
3. Plug the sensor harness into the transmitter
assembly and check that no components are
touching the enclosure. Restore power and allow
a minimum of 30 minutes for stabilization before
adjustment.
4. Connect a DVM across TP10 and GT1 on the
transmitter assembly. Figure 7-10
5. Locate the gain potentiometer which is on the
sensor electronics directly behind one of the holes
in the sensor body. The potentiometer is
accessible by inserting a jewelers screwdriver
through the hole in the sensor.
6. Determine the correct value to be read at TP10
based on the following formula:
VTP10 = 2(C/R) , where C = concentration of span gas,
and R = range of detection (100 PPM).
7. Apply span gas. Adjust the gain potentiometer
until TP10 = correct value as described above.
To increase voltage at TP10 turn the gain
potentiometer counter clockwise.
8. Remove system power and re-install the sensor
and transmitter in the enclosure. Restore power
and calibrate.
Figure 7-10
Hydrogen Sulfide Transmitter Component Locator